Packet networking is a form of data communication in which data packets are routed from a source device to a destination device. Packets can be networked directly between a source node and a destination node, or the packets can be relayed through a number of intermediate nodes.
A wireless network can include a wireless device being connected to a network through a base station that is wired to the network. The wireless device can transmit data packets that are received by the base station and then routed through the network. The wireless network can include many base stations that are each wired to the network.
A wireless device may be mobile, and therefore, require access to more than one base station. When the wireless device travels from an access range of a first base station to an access range of a second base station, a handoff must occur as the connection between the wireless device and the first base station stops, and a new connection between the wireless device and the second base station begins.
An advanced mobile phone system (AMPS) employs a centrally coordinated approach to accomplish handoffs as a mobile phone roams from on cell (defined by a base station) to another cell. When a connection to a mobile phone is to be made, a mobile telephone switching office (MTSO) attempts to locate the mobile phone by instructing all cell sites to page the mobile phone. If the MTSO is connected to a large number of cell sites, and there are a large number of mobile phones, the number of pages is substantial. Handoffs are requested by the mobile device (phone). This approach requires a centralized control which makes it non-scalable. Additionally, this approach requires intelligence within the mobile device so that the device can signal the MTSO when a handoff is necessary. Additionally, routing can be inefficient.
Another approach to wireless accessing is Mobile IP. Mobile IP requires the existence and participation of the following network entities: a Home Agent (HA), a Foreign Agent (FA) and a Mobile Node (MN). In addition, there is a Correspondent Host (CH) that seeks to exchange traffic with the Mobile Node (MN). The Home Agent is charged with keeping track of the physical location of the MN at any point in time and establishing and maintaining a tunnel to an FA near the MN. Any data traffic arriving at the HA for the MN, is routed through the tunnel to the FA. The FA is required to register new MN's and inform the corresponding HA, set up and maintain a tunnel for each MN to its HA and forward data traffic between the MN and its HA through the tunnel. The MN is responsible for Agent Discovery (detecting the local FA) and Registration (registering with the local FA). This approach has several limitations.
The two network entities (HA and FA) are required to be equipped with Mobile IP software for operation of the protocol. Mobile IP MN software has to be loaded on the client device. The HA may be physically far away from the FA. Therefore, considerable latencies may be incurred in routing the data traffic over the tunnel. In particular, this means that applications with low latency requirements such as voice or video will not be well served by this approach. This also approach suffers from a “triangle routing problem”. That is, if the Home Agent is not on the direct path between the Correspondent Host (CH) and the FA, then data traffic between the CH and the MN will travel a circuitous path, resulting in increased latencies and traffic inefficiencies. Packets received for the MN before the MN has registered at the new FA are discarded by the HA. In the case of TCP sessions, these lost packets may trigger a Slow Start/Congestion Avoidance phase that leads to dramatically reduced end-to-end throughput. While the route switches between forwarding and the final route, some out-of-order packets may be generated, affecting the performance of TCP-based applications as well as multimedia traffic that rely on mostly-in-order packet delivery and reasonably consistent end-to-end performance. While this approach may be expected to work sufficiently well for macro-mobility scenarios, the overhead of routing traffic through a tunnel may be overkill for a situation where a mobile device is roaming quickly within a small geographic area (micro-mobility). These two application scenarios are sometimes also described as nomadicity and mobility.
A wireless mesh network includes wireless access nodes interconnected by a mesh of wireless links. Generally, mesh networks suffer from the same handoffs limitations as the mobile phone system. More specifically, handoffs require specific hardware and software within the mobile device to support handoffs within the wireless network.
It is desirable to have a wireless mesh network that allows wireless handoffs of a client between access nodes of different subnets of the mesh network, and does not require the client to include special hardware or software. The mesh network should support nomadicity as well as mobility. It is desirable that the network be able to track clients as the clients roam through the network. Additionally, the network should be fault tolerant.